In impact tools a mass is made to rotate, generally by using a compressed air driven motor, and the momentum of the rotating mass is transferred to an output member to fasten a bolt or nut. A major benefit of such tools is their ability to revolve the output member rapidly under no load and to achieve high torque when turning the bolt or nut home to complete a joint without the operator experiencing appreciable reaction forces. The momentum of the mass is transferred by a dog-clutch type of mechanism which transfers the momentum over typically a 5.degree. turn of the output member before disengaging to enable the mass to once more build up rotating momentum.
Hitherto torque has been controlled generally by calibrating the impact tool to ensure that it generates the necessary torque after applying it for a given time. On the tool itself the impact action is brief and violent and the spinning speeds are high so discouraging attempts to measure torque. Although impact tools can be calibrated to give certain levels of impact, the calibrated level of impact may be difficult to maintain due to compressed air pressure fluctuations. The tightness of a joint can also be influenced by the varying nature of joints some of which may require a prolonged period of impact operation before their completion (so-called soft joints).
It is the object of the invention to provide a system for torque transducing on impact tools which is reliable and can be used on the impact tool to enable a predetermined torque output and predetermined joint strengths to be obtained.